US6576531B2 - Method for cutting semiconductor wafers - Google Patents

Abstract

Improperly mounted wafer saw blades can damage wafers cut or diced with the blades. Embodiments of this invention employ sensors to measure a distance to the blade to help indicate if the blade is improperly mounted. In one method of the invention, the distance to the blade face is measured as the blade is rotated and a variance in this measured distance is determined. If the variance is no greater than a predetermined maximum, the blade may be used to cut the wafer. In one apparatus of the invention, a wafer saw include a blade and a sensor. The sensor is adapted to monitor a distance to a face of the rotating blade. A processor coupled to the sensor may indicate if the distance to the face of the blade as it rotates deviates too far from a baseline position of the blade face.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims foreign priority benefits of Singapore Application No. 200105173-9 filed on Aug. 24, 2001.

TECHNICAL FIELD

The present invention generally relates to devices and methods for cutting microelectronic devices, such as in dicing semiconductor wafers into individual dies.

BACKGROUND

An individual microelectronic component or die is usually formed from a larger substrate, typically a semiconductor wafer. Wafers most commonly are formed primarily from silicon, although other materials such as gallium arsenide and indium phosphide are also sometimes used. Semiconductor wafers have a plurality of dies arranged in rows and columns. Typically, the wafer is sawed or “diced” into discrete dies by cutting the wafer along mutually perpendicular sets of parallel lines or “streets” lying between the rows and columns.

In a typical dicing operation, a semiconductor wafer is attached to a carrier, such as by use of an adhesive, and the carrier is mounted on a table of wafer saw. The wafer saw includes a rotating dicing blade which is attached to a rotating spindle. The dicing blade has a peripheral cutting edge which may be coated with diamond particles or other abrasives to assist in cutting the semiconductor wafer. As the blade of the wafer saw is rotated, it cuts at least partially through the thickness of the wafer and is carefully guided along the streets between adjacent dies. The blade may be guided along these streets by moving the blade relative to the wafer, by moving the table of and the wafer relative to the blade, or by moving both the table and the blade.

If a blade is not precisely mounted on the spindle, the peripheral edge of the rotating blade can trace an irregular path with respect to the axis of rotation of the spindle. Commonly, a blade will be mounted with a flat blade surface clamped flush against a flat surface of a mounting hub carried by the spindle. If the blade is not properly clamped against the hub, any play in the attachment of the blade to the spindle may cause the peripheral cutting edge of the blade to oscillate or waver irregularly. Sometimes a foreign particle can become wedged between the mounting hub and the face of the blade or the mounting hub or the blade may have a burr on its surface. Such a foreign particle or burr can cause the blade to be mounted at an angle. As the shaft is rotated, the path scribed by the peripheral cutting edge of the blade will wobble.

Wavering of the blade as the shaft is rotated can cause the blade to deviate outside the intended street on the wafer, damaging dies on one or both sides of the street. Semiconductor wafers also tend to be somewhat brittle. A wavering blade can cause chipping of the surface of the wafer, damaging dies adjacent to the street even if the blade stays within the proscribed width of the street.

The difficulties associated with properly mounting dicing blades is increasing as the semiconductor industry moves toward dual-blade wafer saws. There are two varieties of dual-blade wafer saws on the market today—dual spindle saws (with parallel, side-by-side spindles) and twin spindle saws (with opposed, axially aligned spindles). One such twin spindle wafer saw is shown in FIG. 3 of U.S. Pat. No. 6,006,739, the entirety of which is incorporated herein by reference. Typically, such twin spindle dual-blade wafer saws simultaneously cut the surface of the semiconductor wafer along parallel lines using a pair of parallel dicing blades. The two blades typically have the same diameter and are rotated about a common rotation axis so they will cut the wafer to the same depth. With commercially available dual-blade wafer saws, the operator's access to the area where the blades are mounted is somewhat limited. It is often difficult for the operator to view the blades edge-on and the operator frequently must mount blades looking along or parallel to the axis of rotation. This makes it difficult for the operator to see the mounting hubs to which the blades are being attached, leading to errors in mounting the blades. In addition, it is difficult to visually confirm that both blades are properly mounted. A highly-skilled, experienced operator can sometimes observe unacceptable wobbling of a cutting blade by watching the blade as it rotates. This visual observation is made more difficult if the operator is only able to watch a face of the blade instead of the edge of the blade. In dual-blade saws, an operator's view of the front blade is largely limited to watching the face of the rotating blade and view of the rear blade is usually greatly hindered, if not completely blocked, by superimposition of the front blade between the operator and the rear blade.

SUMMARY

Embodiments of the present invention provide methods useful in cutting a semiconductor substrate, e.g., a semiconductor wafer, and semiconductor wafer saws. One embodiment of the invention provides a method for cutting a semiconductor substrate wherein the semiconductor substrate is positioned with respect to a blade of a saw. The blade is rotated in a first spaced position wherein a peripheral cutting edge of the blade is spaced from the semiconductor substrate. A distance to a face of the blade is measured as the blade is rotated in the first spaced position. A first variance in the measured distance is determined as the blade is rotated. If the first variance is no greater than a predetermined maximum variance, the semiconductor substrate is contacted with the peripheral cutting edge of the blade. The blade may be translated with respect to the semiconductor substrate to cut at least partially through the semiconductor substrate. If so desired, the method may further include terminating rotation of the blade if the first variance is greater than the predetermined maximum variance. One adaptation of this embodiment includes positioning the blade in a second spaced position after cutting the semiconductor substrate. The peripheral cutting edge of the blade is spaced from the substrate when the blade is in the second spaced position. The blade is rotated in the second spaced position without cutting the semiconductor substrate, the distance to the face of the blade is measured as the blade is rotated in the second spaced position, and a second variance is determined.

Another embodiment of the invention provides a method of operating a semiconductor substrate saw which includes rotating a blade of the saw without contacting the blade with a flow of liquid. A distance to a face of the blade is monitored as the blade rotates. A first baseline distance to the face of the blade and a first deviation from the baseline distance are determined. An error is indicated if the first deviation is greater than a predetermined maximum deviation. Only if the error is not indicated, a first cut at least partially through a semiconductor substrate is made with the blade while contacting the blade with a flow of liquid, such as a cooling liquid.

A method of exchanging a blade of a semiconductor substrate saw is provided in accordance with another embodiment of the invention. In this method, a used blade is removed from a blade mount carried on a shaft of the saw. A new blade is mounted on the blade mount and the new blade is rotated prior to contacting a semiconductor substrate with the new blade. Prior to contacting the semiconductor substrate with the new blade, a distance to a face of the new blade is monitored as the blade rotates, a baseline distance to the face of the blade and a deviation from the baseline distance are determined, and an error is indicated if the deviation exceeds a predetermined maximum deviation. Only if the error is not indicated, a cut is made at least partially through the semiconductor substrate with the blade.

Another embodiment provides a method of exchanging a blade of a multiple-blade saw which includes a used first blade and a second blade, which may also be a used blade. The used first blade is carried on a first shaft for rotation with the first shaft and the second blade is carried on a second shaft for rotation with the second shaft. The used first blade is removed from the first blade mount and a new first blade is mounted on the first blade mount. The new first blade is rotated in a first position and a distance from a first sensor to a face of the new first blade is monitored as the new first blade rotates in the first position. The first sensor is associated with the second shaft. An indication is made whether a first variance in the monitored distance as the new first blade is rotated exceeds a predetermined maximum first variance. If the first variance is not greater than the maximum first variance, a semiconductor substrate may be contacted with the new first blade and with the second blade. This method may further comprise moving the second shaft and the first sensor laterally with respect to the first shaft, thereby changing the distance from the first sensor to the face of the new first blade.

Another embodiment of the invention provides a semiconductor wafer saw. The saw includes a carrier for a microelectronic workpiece and a driver. A first shaft is coupled to the driver and extends opposite the carrier. The first shaft has a first axis. A first blade mount is carried adjacent an end of the shaft for rotation with the first shaft and a first blade is carried by the first blade mount for rotation with the first blade mount. The first blade has a face and peripheral cutting edge. A sensor is spaced from the first blade and is oriented toward the face of the first blade. The sensor maintains a fixed angular position with respect to the first axis as the first blade is rotated with the shaft and is adapted to measure a distance to the face of the first blade. A processor is operatively coupled to the sensor. The processor is adapted to indicate if the distance to the face of the first blade deviates more than a predetermined permitted deviation from a baseline distance to the face of the first blade as the blade rotates.

Yet another embodiment of the invention provides an alternative semiconductor wafer saw which includes multiple blades. In particular, this wafer saw includes a carrier for a microelectronic workpiece. A first spindle extends opposite the carrier and has a first axis. A first blade is carried by the first spindle for rotation therewith and the first blade has a face and a peripheral cutting edge. A second spindle extends opposite the carrier and has a second axis. A second blade is carried by the second spindle for rotation therewith and the second blade has a face and a peripheral cutting edge. A first sensor is carried by the second spindle and adapted to measured a first distance to the face of the first blade. The first sensor maintains a fixed angular position with respect to the first axis as the first blade rotates about the first axis. A second sensor is carried by the first spindle and is adapted to measure a second distance to the face of the second blade. The second sensor maintains a fixed angular position with respect to the second axis as the second blade rotates about the second axis. A processor is operatively coupled to the first and second sensors. The processor is adapted to indicate if variation of the first distance as the first blade rotates exceeds a predetermined maximum first variation and to indicate if variation of the second distance as the second blade rotates exceed a predetermined maximum second variation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematic side view of a semiconductor substrate saw in accordance with one embodiment of the invention.

FIG. 2 is a schematic isolation view of the encircled portion of FIG.1.

FIG. 3 is a schematic elevation view taken alongline3—3 in FIG.1.

FIG. 4 is a graph schematically illustrating output of the sensor of FIG.1.

FIG. 5 is a schematic side view of a semiconductor substrate saw in accordance with an alternative embodiment of the invention.

FIG. 6 is a schematic top view of the semiconductor substrate saw of FIG.5.

DETAILED DESCRIPTION

Various embodiments of the present invention provide semiconductor substrate saws and methods for operating such saws to cut semiconductor substrates. The following description provides specific details of certain embodiments of the invention illustrated in the drawings to provide a thorough understanding of those embodiments. It should be recognized, however, that the present invention can be reflected in additional embodiments and the invention may be practiced without some of the details in the following description.

Single Blade Saw

FIG. 1 schematically illustrates a semiconductor substrate saw10 in accordance with one embodiment of the invention. This saw10 includes a wafer table14 which can be used to support awafer12. In one embodiment of the invention, the wafer table14 is rotatable and translatable in a fixed horizontal plane. Such wafer tables and mechanisms for controlling their movement are well known in the art and need not be discussed in detail here.

Thesaw10 may also include asupport20 which is positioned adjacent the wafer table14. Thesupport20 can take any desired form. In FIG. 1 thesupport20 is schematically shown as an upright structure extending vertically from a position adjacent the table14, but any structure which properly positions theblade40 with respect to thewafer12 will suffice. Thesupport20 in FIG. 1 is shown as enclosing adriver22. Thedriver22 is operatively coupled to aspindle30 to rotate thespindle30 about its rotational axis A—A. Anysuitable driver22 may be employed. In one embodiment, thedriver22 is an electric motor which can be electronically controlled by aprocessor60.

Thespindle30 may be carried by thesupport20 in any desired fashion. In certain embodiments, thespindle30 is movable with respect to the support along one or more axes. In one such embodiment, thespindle30 is adapted to move toward the wafer table14 and away from the wafer table14 under control of theprocessor60. For the wafer saw10 of FIG. 1 wherein the wafer table14 is generally horizontal, this motion of thespindle30 may comprise substantially vertical movement. Thespindle30 may also be adapted to extend outwardly from and retract inwardly toward thesupport20, such as by moving laterally generally along the rotational axis A—A of thespindle30. In the illustrated embodiment, the rotational axis A—A is substantially parallel to the horizontal plane of the wafer table14 and the spindle moves horizontally along this axis A—A.

Anysuitable spindle30 may be employed. In one embodiment, thespindle30 comprises ashaft32 which may be coupled to thedriver22. A mountinghub34 having a mountingface35 may be carried adjacent an end of theshaft32 spaced away from thesupport20. The mountingface35 should be substantially planar and may be polished to a smooth finish. The mountingface35 of the mountinghub34 should have a known orientation with respect to the rotational axis A—A of thespindle30. Preferably, theface35 is substantially perpendicular to the rotational axis A—A.

Thespindle30 may include a mounting mechanism for firmly mounting ablade40 against the mountinghub34. This mounting mechanism may take any suitable form. In FIGS. 1 and 2, the mounting mechanism is schematically illustrated as a retainingnut36. The retainingnut36 or other mounting mechanism is adapted to releasably retain ablade40 on thespindle30. The retaining nut may engage anouter face44 of theblade40 and tightly clamp a mountingface42 of theblade40 against the mountingface35 of the mountinghub34. In ordinary operation, the portion of the mountingface42 of theblade40 covered by the mountinghub34 will have a smooth, flat surface which is adapted to mate flush against the mountingface35 of the mountinghub34.

Any conventional semiconductor substrate cutting blade may be used as theblade40. As noted previously, many such cutting blades include aperipheral edge46 adapted to cut thewafer12 or other semiconductor substrate. A wide variety ofsuch blades40 are commercially available.

In operating a conventional wafer saw, theblade40 and thewafer12 are contacted with a flow of a cooling liquid, such as deionized water, to minimize damage to thewafer12 due to localized overheating. In thesaw10 of FIG. 1, this flow of water or other cooling liquid may be delivered through awater line16. To prevent the water from spraying as the blade rotates and to help protect the blade from inadvertent damage during rotation, ashroud38 may be provided over an upper portion of theblade40. The shroud may take any desired form. In the illustrated embodiment, the shroud covers an outer peripheral portion of theblade40. The location of theshroud38 should be selected to avoid any interference in measurement of the distance D by thesensor50, discussed below.

If theblade40 is properly mounted on thespindle30, the mountingface42 of theblade40 should rotate in a plane which is substantially perpendicular to the rotational axis A—A of thespindle30. If theblade40 is not properly clamped between the retainingnut36 and the mountinghub34, however, theblade40 may shift slightly as it cuts thewafer12. This can lead to somewhat erratic movement of theperipheral cutting edge46 of theblade40, risking damage to thewafer12, as noted above.

FIG. 2 schematically illustrates another problem, which may be encountered in mounting theblade40 on thespindle30. In FIG. 2, a burr B extends outwardly from the mountingface35 of the mountinghub34 and abuts the mountingface42 of theblade40. (It should be understood that FIG. 2 is not drawn to scale and the size of the burr B has been exaggerated for purposes of illustration.) Such a burr B may arise due to inadvertent damage to the mountingface35 of the mountinghub34 or to theblade40. As shown in FIG. 2, the burr B prevents the mountingface42 of theblade40 from lying flush against the mountingface35 of the mountinghub34. As a consequence, theblade40 is not oriented perpendicular to the rotational axis (A—A in FIG. 1) of thespindle30. As a consequence, the point of contact between theperipheral cutting edge46 and thewafer12 will shift from side to side as theblade40 is rotated. This can chip or otherwise damage thewafer12 being diced. While FIG. 2 schematically illustrates a burr B between the mountinghub34 and theblade40, much the same situation can arise if some foreign article becomes trapped between theblade40 and the mountinghub34 as theblade40 is mounted on thespindle30.

Thesaw10 of FIG. 1 also includes asensor50 which is adapted to measure a distance of theblade40 as theblade40 rotates about the rotational axis A—A. In one embodiment, thesensor50 is adapted to measure the distance from thesensor50 to the mountingface42 of theblade40 without any direct physical contact with theblade40. This may be accomplished, for example, by directing a beam of radiation at theblade40 and measuring the reflection of that radiation by theblade mounting face42. Any of a variety of non-contact distance measurement devices can be employed as thesensor50 if they are suitably sensitive. In one useful embodiment of the invention, thesensor50 comprises a CCD laser displacement sensor, such as a LK-2500 series sensor available from Keyence Corporation, Osaka, Japan.

Thesupport50 is adapted to maintain a fixed angular relationship with respect to the rotational axis A—A of thespindle30 as thespindle30 rotates about that axis A—A. In the embodiment of FIG. 1, thesensor50 is shown as being carried by thesupport20. While this ensures that the angular relationship between thesensor50 and the rotational axis A—A remains fixed, it should be noted that the distance between thesensor50 and theblade mounting face42 will vary over time, even if the blade is ideally mounted on thehub34, as thespindle30 is translated inwardly and outwardly with respect to thesupport20 along the rotational axis A—A.

Thesensor50 is adapted to monitor the distance D from thesensor50 to theblade mounting face42. In one embodiment of the invention, thesensor50 monitors the distance D during the entire operation of thesaw10 as it cuts thewafer12. Cooling water on theblade mounting face42 can interfere with accurate readings of the distance D in some embodiments, though. In an alternative embodiment, thesensor50 measures the distance D to the mountingface42 only at selected times, as described below.

FIG. 4 schematically illustrates three idealized plots of the distance D between thesensor50 and theblade mounting face42 for three different circumstances. In an idealized condition wherein theblade mounting face42 is perfectly flat and theblade40 is perfectly mounted on the mountinghub34, the distance D will not vary at all as theblade40 is rotated unless thespindle30 is translated along the rotational axis A—A. This idealized circumstance is represented by a straight line A in FIG.4. The dashed curve C in FIG. 4 illustrates a plot of the distance D as a function of time t for an improperly mountedblade40, such as theblade40 shown in FIG.2. This curve C is generally sinusoidal, with a period P which represents one complete revolution of theblade40 about the rotational axis A—A. During the course of each period P, the distance D varies from a maximum reading to a minimum reading. This variation in the distance D may be considered a variance V_cfor the curve C. The average distance D_avgof the curve C may be thought of as a baseline distance from thesensor50 to theblade mounting face42. The actual distance D will vary about this baseline distance D_avg, as the blade rotates, with the maximum change from this baseline distance being a deviation D_cfor the curve C.

If the variance V_cexceeds a predetermined maximum variance V_max, theblade40 may be considered improperly mounted on thespindle30. Likewise, if the deviation D_cof the curve C exceeds a predetermined maximum deviation D_max, this can be taken as an indication that theblade40 is likely improperly mounted on thespindle30. The maximum permitted variance V_max, and/or deviation D_max, may be selected to materially reduce the likelihood of inadvertent damage to thewafer12, while permitting reasonable tolerances in the mounting hub.34, theblade40, thespindle30, and the fit of theblade40 on thehub34. In one embodiment, for example, the maximum permitted variance V_max, is about 2 μm and the maximum permitted deviation D_maxis about 1 μm.

The data from thesensor50 may be delivered to theprocessor60. Theprocessor60 may comprise any suitable structure which is adapted to process the signal from thesensor50. For example, theprocessor60 may comprise a computer running a program adapted to process the signal from thesensor50. If theprocessor60 determines that the variance V_cas the blade rotates exceeds the maximum permitted variance V_max, or if the deviation D_cexceeds the maximum permitted deviation D_max, theprocessor60 may indicate an error condition. This can be communicated in any desired fashion. For example, the processor may deliver a warning signal to the operator on adisplay62 connected to theprocessor60. Alternatively or in addition to the output on thedisplay62, the warning signal may comprise an audible and/or visible alarm signal on analarm64 connected to theprocessor60. This warning signal may be designed to get the attention of a human operator so the operator can inspect thesaw10 and intervene in its operation, if necessary. In another embodiment, theprocessor60 is adapted to terminate rotation of thespindle30 by thedriver22 if the variance V_cexceeds the maximum permitted variance V_max, or if the deviation D_cexceeds the predetermined maximum deviation D_max. Terminating rotation of theblade40 in this fashion can limit or prevent damage to thewafer12 by contact with an improperly mountedblade40.

FIG. 4 shows an intermediate dotted curve B which schematically illustrates ablade40 operating within acceptable operating parameters. The curve B is not a straight horizontal line representing no change at all in the distance D from thesensor50 to theblade mounting face42 as in curve A. However, the variance V_Bof the curve B is less than the maximum permitted variance V_max. Similarly, the deviation D_Bof the curve B is less than the maximum permitted deviation D_max. If the maximum permitted variance V_maxand/or the maximum deviation D_maxare appropriately selected, ablade40 exhibiting a variance V_Band a deviation D_Bas shown in curve B can be used to cut thewafer12 with little or no inadvertent damage to thewafer12.

FIG. 3 schematically illustrates a relationship between the position of thesensor50 and the mountingsurface42 of theblade40. For a given angular displacement of theblade40 from a flush mount against the hub mounting face (35 in FIG.2), the variation in the distance (D in FIG. 1) between thesensor50 and theblade mounting surface42 will depend on the location of thetarget area52 of thesensor50 on theblade mounting surface42. If thesensor50 is oriented to detect the distance to atarget area52 positioned adjacent theperipheral cutting edge46 of theblade40, the change in the distance D will be at or near its maximum for a given angular displacement of theblade40 from a flush mount against thehub34. If the sensor is instead oriented toward atarget area52′ positioned closer to the center of the blade, the variation in the distance D between thesensor50 and the mountingface42 at that location will vary less for the same angular displacement of theblade40 from a proper mounting position. If the sensor is adapted to move with thespindle30 as the spindle rotational axis A—A moves with respect to the wafer table14, thesensor50 will always be oriented toward thesame target area52 on theblade mounting face42. If, however, the sensor remains stationary as the distance between the axis A—A and the wafer table14 is varied, thesensor target location52 on theblade mounting face42 will vary. If the processor monitors the relative position of thespindle30 to the wafer table14 over time, however, the processor can determine the radius of thesensor target area52 from the center of theblade40 and adjust the acceptable operating parameters accordingly. Hence, the maximum permitted variance V_maxand the maximum permitted deviation D_maxwill be less for thetarget area52′ with a radius R₂from the center of theblade40 than they will be for thetarget area52 with a larger radius R₁.

Dual-Blade Saw

FIGS. 5 and 6 schematically illustrate a twin spindle dual-blade semiconductor substrate saw110 in accordance with an alternative embodiment of the invention. The structure and operation of this saw110 bears significant resemblance to the structure and operation of thesaw10 shown in FIGS. 1-3. Two distinctions between these two designs are worth noting, though. First, thesaw110 of FIG. 5 has a pair ofblades140aand140brather than asingle blade40. Second, thesensors150aand150bof thesaw110 are adapted to move with respect to thesupports120aand120brather than being permanently affixed to thesupport20.

Thesaw110 of FIGS. 5 and 6 is shown as having a pair of supports120aand120b, each of which houses aseparate driver122aand122b. If so desired, both of thespindles130aand130bmay be coupled to a common driver122 and/or supported by a common support120. If separate drivers122a-bare utilized, their operation can be coordinated by theprocessor160.

As with the prior embodiment, afirst spindle130amay comprise ashaft132a, a mountinghub134aand a retainingnut136afor mounting thefirst blade140a. Similarly, asecond spindle130bmay include ashaft132b, a mountinghub134b, and a retainingnut136bto mount thesecond blade140b.

A wafer table114 may position awafer112 in proximity to the blades140a-bso the blades140a-bcan make a cut in thewafer112. (Four such cuts, designated by reference numerals1-4, are schematically shown in FIG. 6.) In FIGS. 5 and 6, each of the blades140a-bis shown as having aseparate water line116aor116b. If desired, a single water line can be used to deliver a flow of water or other cooling liquid to both of the blades140.

The dual-blade saw110 of FIGS. 5 and 6 utilizes aseparate sensor150aor150bto measure a distance to an associated one of theblades140aor140b, respectively. If so desired, one or both of these sensors150a-bcan be carried by thesupport120aor120bassociated with theblade140aor140btoward which thesensor150aor150b, respectively, is directed. In the illustrated embodiment, however, thesensor150aor150bfor eachblade140aor140bis carried by theshroud138bor138afor theopposite blade140bor140a. In particular, theshroud138aassociated with thefirst blade140acarries thesecond sensor150bfor measuring a distance to theouter face144bof thesecond blade140b. Similarly, thesecond shroud138bcarries thefirst sensor150afor measuring a distance to theouter face144aof thefirst blade140a.

The sensors150a-bcan be mounted on their respective shrouds138a-bin any desired fashion and in any suitable location. In the illustrated embodiment, thefirst sensor150ais attached to thesecond shroud138bvia an L-shapedbracket152a. Thisbracket152ais positioned toward one edge of theshroud138band extends downwardly beyond the bottom edge of theopposite shroud138a. This orients thefirst sensor150atoward a target area adjacent a periphery of theouter face144aof thefirst blade140a. Theother sensor150bcan be mounted to theother shroud138ausing a similar L-shapedbracket152b. To avoid any interference between the two sensors150a-b, thesecond sensor150bmay be positioned on the opposite side of the shared rotational axis A—A of the spindles130a-b(see FIG.6).

As thesaw110 is operated, it may be desirable to alter the distance between thefirst blade140aand thesecond blade140bto properly align the blades140 along separate streets on the wafer. This distance can be varied by moving one or both of the spindles transversely along their coincident axes. The sensors150a-bare carried on shrouds138a-bwhich are, in turn, carried by the spindles130a-b. Accordingly, as the spindles130 move to alter the distance between the blades140, the distance from the sensors150a-bto their respective blades140a-bwill be altered, as well.

Data from both of the sensors150a-bcan be delivered to acommon processor160. Aspects of performance of the blades140a-bcan be displayed on thedisplay162. If the distances measured by the sensors150a-bfall outside of acceptable operating parameters, a warning signal can be delivered to the operator via analarm164. Instead of or in addition to delivering such a warning signal to thealarm164, theprocessor160 may terminate rotation of one or both of the spindles130a-b. In one embodiment, theprocessor160 terminates rotation only of thespindle130aor130bcarrying theblade140aor140bwhich falls outside of acceptable operating parameters. In an alternative embodiment, theprocessor160 terminates rotation of both spindles130a-bif the data from the sensors150a-bindicates that either one of the blades140a-bis operating outside of acceptable operation parameters.

Methods of Operation

The present invention provides a variety of methods for utilizing a semiconductor substrate saw. For purposes of illustration, reference is made in the following discussion to thesaw110 shown in FIGS. 5 and 6. It should be understood, though, that this is intended solely to aid in understanding the methods and that methods of the invention may be carried out using devices which differ materially from thesaw110 of FIGS. 5 and 6.

One or both of the blades140a-bwill be replaced with a new blade as they near the end of their useful life. Often, both of the blades140a-bwill be replaced at the same time, but it may be necessary to replace one of the blades, such as one of the blades is damaged. To replace thefirst blade140a, the retainingnut136amay be loosened and the shroud138 may be lifted out of the way. The user may then slide the usedfirst blade140aoff thespindle130a. A newfirst blade140amay be positioned on thespindle130a, the retainingnut136amay be tightened to hold the newfirst blade140aon thespindle136a, and theshroud138amay be placed back in its original position about an outer peripheral portion of thefirst blade140a. Thesecond blade140bmay be replaced in much the same fashion.

Once the new blade140 is mounted on its spindle130, the shaft132 of the spindle130 may be rotated. In one embodiment, both of the shafts132a-bare rotated at the same time even if only one of the blades140a-bhas been replaced. As the blades140a-bare rotated, the distance from thesensor150ato theouter face144aof thefirst blade140amay be monitored and the distance from thesecond sensor150bto theouter face144bof thesecond blade140bmay be monitored. Theprocessor160 may receive data from the sensors150a-band determine the variance and/or deviation for each of the blades140a-bgenerally as outlined above in connection with FIG.4. If the variance and/or deviation of either of the blades140a-bexceeds the predetermined maximum value V_maxor D_max, respectively theprocessor160 may indicate an error on thedisplay162 or via thealarm164. Alternatively or in addition to indicating such an error, theprocessor160 may terminate rotation of one or both of the blades140a-b.

The blades140a-bmay be replaced with the spindles130a-bspaced sufficiently above the wafer table114 to space the peripheral cutting edges146a-bof the blades140a-babove the surface of anywafer112 in the wafer table114. In one embodiment, the blades140a-bare rotated with the spindles130a-bin these elevated positions and before the newly mounted blade(s) are lowered into contact with awafer112. This will help identify any problems with the mounting of the blades140a-bbefore an improperly mounted blade140a-bis allowed to damage thewafer112. In one adaptation of this method, the first and second blades140a-bare lowered into contact with thewafer112 only if the blades140a-bare operating within acceptable parameters and theprocessor160 does not indicate any error. Rather than leaving this function entirely to theprocessor160, theprocessor160 may simply indicate any error to an operator and the operator can determine whether to lower the blades140a-binto cutting contact with thewafer112.

In cutting thewafer112, the peripheral cutting edges146a-bof both of the rotating blades140a-bcan be brought into contact with a surface of thewafer112. By controlling the distance of the spindles130a-bfrom the wafer table114, the depth of the cuts by the blades140a-bcan be controlled. In some circumstances it may be desirable to cut only partially through thewafer112 rather than through its entire thickness. After the partial cut has been made, thewafer112 may be broken along the kerfs left by the blades140a-b.

Depending on the nature of the sensors150, an undue amount of fluid on the outer faces144 of the blades140 may interfere with precise measurement of the distance to the blade outer face144. Hence, in one embodiment, thenew blades140aand140bare rotated and the distance is monitored using the sensors150 before the blades140 are brought into contact with a flow of water or other cooling liquid from the water lines116a-b.

It may be desirable to check the status of the blades140a-bfrom time to time to ensure that they remain properly mounted on their respective spindles130a-b. It may be possible to monitor the distance from each sensor150a-bto its associated blade140a-bwhile the blade is used to cut awafer112. In an embodiment of the invention, however, the processor will indicate an error and/or terminate rotation of the blades only when the blades are not cutting awafer112. In accordance with one specific embodiment, the spindles130a-bare moved away from the wafer table114 to space the peripheral cutting edges146 of the blades140 from thewafer112. The spindles130 may be returned to the same position with respect to the wafer table114 they occupied when the new blades140 were installed on the spindles130. In an alternative embodiment, the blades140 may be mounted on their respective spindles130 at a first elevation and the proper mounting of the blades.140 on the spindles130 may be confirmed before the spindles are lowered toward thewafer112. The later confirmation that the blades140 remain properly mounted can be performed at a different elevation, such as at a position closer to the wafer table114. In one embodiment, the blades140 are spaced sufficiently from the wafer table114 and the water lines116 to ensure that the blades are not in contact with a continuous flow of the cooling liquid. At this elevation, the spindles130 may be rotated and the distance from each of the sensors150a-bto their respective blades140a-bcan be monitored.

Theprocessor160 may preclude lowering the blades140 back into contact with thewafer112 if the second mounting check finds that the measured distances to the blades140 no longer fall within acceptable operating parameters. It may be possible to perform a second check after making a first series of cuts in thewafer112 without interfering with normal operation of thesaw110. For example, it is common practice in the industry to check the cuts or kerfs (1-4 in FIG. 6) already formed in thewafer112 from time to time to ensure that thewafer112 is being diced properly. The interim, post-cutting measurement of the blade mounting using the sensors150 can be performed during such a routine lull in cutting.

In one embodiment of the invention, both of the blades140 are returned to a specific, pre-defined location each time the mounting of the blades140 is to be checked with the sensors150. Returning to a specific location each time is not required, though. The variance and deviation measurements help identify irregularities in the motion of the blade as it rotates and these measurements are independent of the actual baseline distance (D_avgin FIG.4). As a consequence, an improperly mounted blade can be identified even if the baseline distance D_avgbetween a sensor150a-band the associated blade140a-bdiffers from one measurement to the next. As a consequence, the distance between the blades140a-bcan be varied to cut along different streets on thewafer112 and the mounting of the blades140 can be checked without having to return the blades to a home position. In the single-blade saw10 of FIG. 1, the mounting of theblade40 on thespindle30 can be checked without having to move theblade40 to a specific location with respect to thesupport20. The ability to check the mounting of the blades140a-bor40 without returning them to a fixed position each time eliminates additional blade movements, helping ensure more precise registration of theblades140 or40 with the streets on thewafer112.

From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.

Claims (39)

What is claimed is:

1. A method of cutting a semiconductor substrate, comprising:

positioning the semiconductor substrate with respect to a blade of a saw;

rotating the blade in a first spaced position wherein a cutting edge of the blade is spaced from the semiconductor substrate;

measuring a distance to a face of the blade as the blade is rotated in the first spaced position and determining a first variance in the measured distance as the blade is rotated, the/first variance being indicative of irregularities in the motion of the blade as it rotates; and, if the first variance is no greater than a predetermined maximum variance,

contacting the semiconductor substrate with the cutting edge of the blade and translating the blade with respect to the semiconductor substrate to cut at least partially through the semiconductor substrate.

2. The method ofclaim 1 further comprising terminating rotation of the blade if the first variance is greater than the predetermined maximum variance.

3. The method ofclaim 1 further comprising generating a warning if the first variance is greater than the predetermined maximum variance.

4. The method ofclaim 1 wherein the first variance is determined without contacting the blade with a flow of cooling liquid.

5. The method ofclaim 4 wherein the blade is contacted with a flow of cooling liquid when the blade is cutting the semiconductor substrate.

6. The method ofclaim 1 wherein the blade is rotated in the first position prior to contacting the semiconductor substrate with the blade.

7. The method ofclaim 1 further comprising positioning the blade in a second spaced position after cutting the semiconductor substrate, the cutting edge of the blade being spaced from the semiconductor substrate when the blade is in the second spaced position; rotating the blade in the second spaced position without cutting the semiconductor substrate; measuring the distance to the face of the blade as the blade is rotated in the second spaced position and determining a second variance that is indicative of irregularities in the motion of the blade as it rotates.

8. The method ofclaim 7 wherein the first spaced position is the same position as the second spaced position.

9. The method ofclaim 7 further comprising contacting the semiconductor substrate with the cutting edge of the blade if the second variance is no greater than the predetermined maximum variance.

10. The method ofclaim 7 further comprising terminating rotation of the blade if the second variance is greater than the predetermined maximum variance.

11. The method ofclaim 7 further comprising generating a warning if the second variance is greater than the predetermined maximum variance.

12. A method of operating a semiconductor substrate saw, comprising:

rotating a blade of the saw without contacting the blade with a flow of liquid;

monitoring a distance to a face of the blade as the blade rotates;

determining a first average baseline distance to the face of the blade and determining a first deviation from the first average baseline distance as the blade rotates;

indicating an error if the first deviation is greater than a predetermined maximum deviation; and, only if the error is not indicated,

making a first cut at least partially through a semiconductor substrate with the blade while contacting the blade with a flow of liquid.

13. The method ofclaim 12 further comprising terminating rotation of the blade if an error is indicated.

14. The method ofclaim 12 further comprising generating a warning if an error is indicated.

15. The method ofclaim 12 wherein the first cut is made by contacting the semiconductor substrate with a peripheral cutting edge of the blade.

16. The method ofclaim 15 wherein the liquid comprises water.

17. The method ofclaim 12 wherein the distance to the face of the blade is monitored when the blade is in a first position, the blade in the first position being spaced from the semiconductor substrate.

18. The method ofclaim 12 further comprising positioning the blade in a spaced position with a cutting edge of the blade spaced from the semiconductor substrate; rotating the blade in the spaced position without cutting the semiconductor substrate; monitoring a distance to the face of the blade as the blade is rotated in the spaced position; and determining a second average baseline distance to the face of the blade and determining a second deviation from the second average baseline distance.

19. The method ofclaim 18 further comprising making a second cut at least partially through the semiconductor substrate only if the second deviation is no greater than the predetermined maximum deviation.

20. The method ofclaim 18 further comprising terminating rotation of the blade if the second deviation is greater than the predetermined maximum deviation.

21. The method ofclaim 18 further comprising generating a warning if the second deviation is greater than the predetermined maximum deviation.

22. The method ofclaim 1 wherein the distance to the face of the blade is measured with a sensor, the blade of the saw being adapted to move transversely with respect to the sensor.

23. The method ofclaim 22 further comprising moving the blade transversely with respect to the sensor.

24. The method ofclaim 1 wherein the distance to the face of the blade is measured with a sensor, further comprising moving the blade transversely with respect to the sensor to a second spaced position after cutting the semiconductor substrate; rotating the blade in the second spaced position; measuring the distance to the face of the blade as the blade is rotated in the second spaced position and determining a second variance that is indicative of irregularities in the motion of the blade as it rotates.

25. The method ofclaim 12 wherein the distance to the face of the blade is measured with a sensor, the blade of the saw being adapted to move transversely with respect to the sensor.

26. The method ofclaim 25 further comprising moving the blade transversely with respect to the sensor.

27. The method ofclaim 12 wherein the distance to the face of the blade is measured with a sensor, further comprising moving the blade transversely with respect to the sensor to a second spaced position after cutting the semiconductor substrate; rotating the blade in the second spaced position; measuring the distance to the face of the blade as the blade is rotated in the second spaced position and determining a second average distance and a second deviation from the second average distance as the blade is rotated, the second average distance being different from the first average distance and the second deviation being indicative of irregularities in the motion of the blade as it rotates.

28. A method of cutting a semiconductor substrate, comprising:

positioning the semiconductor substrate with respect to a blade of a saw;

rotating the blade in a first spaced position wherein a cutting edge of the blade is spaced from the semiconductor substrate;

measuring a distance to a face of the blade with a sensor as the blade is rotated in the first spaced position and determining a first average distance to the face of the blade and a first deviation from the first average distance as the blade is rotated, the first deviation being indicative of irregularities in the motion of the blade as it rotates; and,

if the first deviation is no greater than a maximum permitted deviation, contacting the semiconductor substrate with the cutting edge of the blade and translating the blade with respect to the semiconductor substrate to cut at least partially through the semiconductor substrate; or

if the first deviation is greater than the maximum permitted deviation, indicating an error.

29. The method ofclaim 28 wherein indicating an error condition comprises terminating rotation of the blade.

30. The method ofclaim 28 wherein indicating an error condition comprises generating a warning.

31. The method ofclaim 28 wherein the first deviation is determined without contacting the blade with a flow of cooling liquid.

32. The method ofclaim 31 wherein the blade is contacted with a flow of cooling liquid when the blade is cutting the semiconductor substrate.

33. The method ofclaim 28 further comprising positioning the blade in a second spaced position after cutting the semiconductor substrate, the cutting edge of the blade being spaced from the semiconductor substrate when the blade is in the second spaced position; rotating the blade in the second spaced position without cutting the semiconductor substrate; measuring a second average distance to the face of the blade as the blade is rotated in the second spaced position and determining a second deviation from the second average distance as the blade is rotated, the second deviation being indicative of irregularities in the motion of the blade as it rotates.

34. The method ofclaim 33 wherein the first spaced position is the same position as the second spaced position.

35. The method ofclaim 33 further comprising contacting the semiconductor substrate with the cutting edge of the blade if the second variance is no greater than the predetermined maximum variance.

36. The method ofclaim 33 further comprising terminating rotation of the blade if the second variance is greater than the predetermined maximum variance.

37. The method ofclaim 33 further comprising generating a warning if the second variance is greater than the predetermined maximum variance.

38. The method ofclaim 28 further comprising moving the blade transversely with respect to the sensor.

39. The method ofclaim 28 further comprising moving the blade transversely with respect to the sensor to a second spaced position after cutting the semiconductor substrate; rotating the blade in the second spaced position; measuring the distance to the face of the blade as the blade is rotated in the second spaced position and determining a second average distance and a second deviation from the second average distance as the blade is rotated, the second average distance being different from the first average distance and the second deviation being indicative of irregularities in the motion of the blade as it rotates.

Images